The present invention relates to a cellular communication system supporting packet data communication and including a number of packet data nodes controlling the packet data communication in a number of packet paging areas. The packet data nodes comprise mobile station information handling means keeping information about mobile stations registered in the cells covered by the packet paging areas in turn covered by the packet data node and cell information handling means keeping information about the packet data communication channels in the cells covered by the packet data node and means for paging mobile stations.
The invention also relates to an arrangement for paging mobile stations in a stand-by state in a cellular communication system supporting packet data communication. Still further the invention relates to a method of paging mobile stations in a stand-by state in a cellular communication system supporting packet data communication.
When a mobile station has been inactive for a predetermined time period, meaning that no packets have been received from a mobile station in a packet data node or transmitted to a mobile station, the mobile station enters a so called stand-by state or a packet stand-by state. One of the reasons for introducing such a stand-by state is to increase the life time of the battery used in the mobile station. A mobile station in stand-by state does not have to inform the network, or a packet data node, when it changes from one cell to another, but it only has to inform the network when it changes packet paging area. When a mobile station is in a stand-by state, it only listens to one intermittently sent time slot for packet paging messages. A cell may for example be divided into a number of packet paging groups each of which being assigned a particular time slot for paging messages. For example, in the PDC (Pacific Digital Communication) system the mobile station then only listens to one time slot per superframe for packet paging messages. This is described in RCR STD 27F, Personal Digital Cellular Telecommunication System ARIB Standard, issued April 30th, 1991 and last revised Feb. 18th, 1997, by Association of Radio Industries and Business. If the network, or particularly the packet data node, needs to transfer information to mobile stations being in the packet stand-by state, the network, or the node, has to wake-up the mobile stations by transmitting a packet paging message to the mobile stations in the respective packet paging group time slot assigned for paging of the mobile stations. If for example the cell parameters in a cell have been changed, i.e. the number of packet data communication channels, or particularly the time slot(s) used for packet data communication in a cell, the network (the packet data node) has to broadcast information about the new cell parameters in the changed cell. A reason for changing the cell parameters, particularly the packet data communication channel resources, may be that the traffic load in the cell changes. The packet data node then uses the time slot assigned to the packet common group for such information. The packet data nodes of the network will always be informed when a mobile station enters the packet stand-by state and when there is a need to broadcast common information, such as the cell parameters, all mobile stations being in the packet stand-by state have to be woken-up. This is done by the packet data node and it transmits a packet paging message which includes information about how many packet common group time slots that will carry the broadcast information. The broadcast information is then transmitted in all time slots of the packet common groups as specified in the paging message. Thus, when information is broadcasted, the packet data node first transmits a packet paging message to wake-up all the mobile stations in the packet stand-by state in the concerned cell. The packet paging message is transmitted on all time slots belonging to the packet paging groups in the cell. The mobile stations on the other hand only listen to one time slot, namely the time slot assigned their own packet paging group. However, if a mobile station is not able to receive the packet paging message, for example depending on the actual physical location of the mobile station; it may for example be somewhere where it can not be reached by the paging message such as in a tunnel, behind a mountain or a large building or similar. Such a mobile station will consequently not receive the common information transmitted by the packet data node or by the network in general. Therefore, every mobile station which does not receive the packet paging message, will be lost by the network and all packet paging attempts by the network to find them will fail. The packet paging message is sent in one time slot in every cell in the packet paging area in which the mobile station is registered. A calculation of which-packet data communication channel, or which time slot(s) or functional channel, UPCH, which is one time slot on a packet data communication channel PPCH, is performed. The calculation of which UPCH(s) are to be used in a cell depends on the configuration of the cell, i.e. the number of packet data communication channels or particularly functional channels of which the packet data communication channels are composed. If the configuration changes, the packet data mode does not know whether the mobile station uses the old or the new configuration (which means the configuration after an update has been done in the cell i.e. after the cell has been upgraded), i.e. it does not know whether the mobile station listens to the xe2x80x9cnewxe2x80x9d or the xe2x80x9coldxe2x80x9d functional channel. Thus, if the data communication resources in a cell are changed the resources to be used by a particular mobile station may be changed and if the mobile station does not receive such information, it will be lost. This is a serious drawback. The situation is different for speech and circuit switched data communication since the mobile stations within a location area continuously listen to the broadcast channel and therefore, for speech and circuit data communication the same problem does not occur.
What is needed is therefore a system, an arrangement and a method respectively through which mobile stations in a stand-by state or particularly packet stand-by state can be paged in a safe and reliable manner with a minimized risk of mobile stations being lost by the network. A system, an arrangement and a method are also needed through which paging of mobile stations can be performed in a fast and efficient manner and without wasting communication resources. A system, an arrangement and a method is also needed to enable an improvement in hitherto known system, or for providing existing systems with a safeguarding mechanism, or a fall-back, in case a mobile station has missed the broadcast information.
Therefore a cellular communication system as referred to above is provided in which each packet data node comprise mobile station information handling means keeping information about the mobile stations registered with the cells covered by the packet paging areas in turn covered by the respective packet data node and cell information handling means for keeping information about packet data communication channels in the cells covered by the packet data node. Means are further provided for calculating which packet data communication channel resources are to be used for the mobile stations after an update (upgrading) of a cell, which means that the (number of) packet data communication channel resources in a cell is altered. Means are provided for paging a mobile station in a stand-by state through the sending of a number of first paging messages from the packet data node using the packet data communication channel resources, as calculated by the calculating means, in all cells within the packet paging area in which the mobile station is registered. The system also includes means for keeping information about whether a mobile station to which a number of first paging messages is/are sent is found or not, and means for sending a second paging message, for mobile stations which have not been found, to all cells which have been updated and on all packet data communication channel rescources of such cells; at least the cells in which the mobile station is not registered.
Particularly a mobile station registered with the packet data node for packet data communication enters a packet stand-by state when no packet data has been communicated to/from the mobile station for a predetermined time period. The packet data node comprises means for keeping information on mobile stations being in the packet stand-by state. Particularly a packet data communication channel using one frequency is composed of a number of functional channels. Each functional channel corresponds to one time slot on said frequency. A packet data communication channel may particularly comprise one, two or three functional channels, or, in other words a packet data communication channel uses one, two or three time slots on one and the same carrier frequency. In the following a packet data communication channel also is referred to as a PPCH (Packet Physical Channel) whereas a functional channel also is referred to as a UPCH (User Packet Channel).
In the calculating means a calculation is performed to calculate which packet data communication channel resource is to be used by a mobile station in a stand-by state after a cell update. The calculating means then calculates which UPCH in the respective cell that is to be used (for paging messages). In an exemplary embodiment a first paging message is sent on the calculated UPCHs in all cells within the packet paging area in which the mobile station is registered. In an alternative embodiment a number of first paging messages are sent in such a manner. In a particular embodiment the number of first paging messages is configurable. Particularly the second paging message is sent on all UPCHs of all packet data communication channels in all updated cells within the packet paging area. In a particular embodiment the mobile station information handling means keeps information about data communication traffic events for the mobile stations in the packet paging area. Hereby is meant information about transmission of data packets to the mobile stations or reception of data packets from the mobile stations in the packet paging area as well as periodical registration messages sent with a given or configurable regularity from the mobile station to the PDN, which may be done also when the mobile is in a stand-by state. The mobile station information handling means further includes means for keeping information about the times at which such events occur.
In an advantageous embodiment the mobile station information handling means includes mobile station time stamping means for stamping the time of each data communication event and at least the latest time stamp, relating to the last event, is stored. Furthermore information about the data communication channel, and particularly the functional channel(s) used at such events, is also stored.
In the exemplary embodiment the cell information handling means keeps information about which packet data communication channels are used in each cell within the packet paging area, including information about which are the UPCHs corresponding to said packet data communication channels and particularly said information handling means includes cell time stamping means for stamping the time when a cell is updated. In a particularly advantageous embodiment the cell information handling means contains a cell update flag which is set when a cell is updated and which is cleared when a time period has elapsed, which time period may be predetermined, fixed or reconfigurable, advantageously the time period for xe2x80x9cflag setxe2x80x9d is longer than the period at which periodical registration messages are sent out by the mobile station.
The packet data node may particularly include a paging timer for which a time interval is given, and upon the expiry of which a second paging message is sent out (unless the mobile station has confirmed that it has received a first paging message). Said paging timer may be initiated upon sending out of a first paging message, or if a number of first paging messages are sent out, e.g. upon sending out of the last first paging message.
Particularly the packet data node includes comparing means for comparing the time stamp of each cell in the packet paging area (or of each cell for which an update flag is set) with the time stamp of the mobile station and the second paging message is provided on all UPCHs in all cells, for which the cell time stamp shows a later time than the mobile station time stamp according to one embodiment.
In an advantageous embodiment the cell information means includes a table or similar keeping information about all cell identities, cell update time stamps, cell update flags, the packet paging areas to which the cell may belong and about which functional channels the packet data communication channels are composed of.
In an alternative embodiment the second paging message is sent on all functional channels of all packet data communication channels of all updated cells in the packet paging area except for the cell in which the mobile station is registered. In that cell, in case it has been updated, the second paging message is sent on the packet data communication channel on which the mobile station is registered and on the packet data communication channel which is calculated by the calculating means. If the mobile station is not found, although it probably will be found, a third paging message may be sent out, in that particular cell only, but on all UPCHs of that cell (possibly with exception of the UPCHs on which the second paging message was sent). In another advantageous embodiment, however, the second paging message is sent on all UPCHs also in that cell. That minimizes the risk of not finding the MS with the second paging message.
Therefore also an arrangement for paging a mobile station in a cellular communication system supporting packet data communication is provided. The arrangement comprises a packet data node, which controls a number of cells grouped into paging areas, and which contains mobile station information handling means keeping information about the mobile stations and cell information handling means is provided keeping information about packet data communication channel resources in the cells. The arrangement furthermore includes calculating means for calculating which packet data communication resources should be assigned to mobile stations after a cell update and paging means is provided for sending a number of first paging message(s) on the new calculated packet data communication channel resource in all cells within the packet paging area in which the mobile station is registered. Furthermore means are provided for detecting whether a mobile station has confirmed reception of the paging message and for sending out a second paging message if no confirmation has been received. The second paging message is sent out to all cells in the packet paging area having been updated and, in one embodiment, on all packet data communication channel resources of such cells. (By all updated cells is meant all cells having been updated after a mobile station has been in contact with the packet data node).
Particularly a packet data communication channel using one frequency is composed of one, two or three functional channels, each of which corresponds to one time slot on the frequency. Advantageously, in the calculating means, is also calculated which functional channel(s) on the packet data communication channel is/are to be used for paging messages to the mobile station. In an exemplary embodiment the first paging message is sent on the calculated functional channels in all cells within the packet paging area. In a particular embodiment this first paging message can be sent out more than once; the number of first paging messages being sent out may be configurable.
In the exemplary embodiment the second paging message is sent on all functional channels of all packet data communication channels in all updated cells within the packet paging area. In a preferred embodiment the mobile station information handling means keeps information about data communication traffic events concerning the mobile station and a mobile station time stamping means is provided for stamping the time at which such events occur. Furthermore cell information handling means keeps information about which PPCHs are used in each cell within the packet paging area, including information about which functional channels of the respective PPCHs that are used and furthermore cell time stamping means are provided for providing a time stamp when the cell is updated. Preferably the packet data node includes a paging timer for which a time interval is given, upon the expiry of which a second paging message is sent out. Said timer is initiated at sending out of the first paging message, or, alternatively, if more than one first paging message is sent out, upon sending out of the last first paging message. Alternatively a number of first paging messages can be sent out during a predetermined time period in which case the timer is initiated upon the first transmission of the first paging message. The second paging message is sent out to all cells in the packet paging area having being time stamped at a later occasion than the concerned mobile station has been time stamped.
Therefore a method of paging a mobile station in a cellular communiation system supporting packet data communication also is provided. It is supposed that the mobile station is registered in a packet paging area controlled by a packet data node. The method then comprises the steps of: sending a number of first paging message(s) to all cells within the packet paging area in which the mobile station is registered using up-to-date packet data communication channels in each cell; examining whether a confirmation is provided that the mobile station has received the first paging message, if no confirmation is provided, for each cell examining whether the cell has been updated since the last contact between the packet data node and the mobile station, and sending a second paging message to all cells having been updated since the last contact between the packet data node and the mobile station, which second paging message is sent on all packet data communication channel resources of such cells with the possible exception of the cell in which the mobile station is registered. The method particularly includes the steps of calculating which packet data communication channel resource the mobile station should use in the cell when the cell has been updated including calculation of which functional channel(s) among a number of functional channels of which the packet data communication channel is composed, the mobile station should use. Still further the method may include sending the first paging message on the calculated functional channel(s) in all cells within the packet paging area and sending the second paging message on all functional channels of all packet data communication channels in all updated data cells within the packet paging area. Particularly the method includes the steps of: stamping the time for packet data communication events relating to the mobile station, stamping each time when a cell is updated, examining which cells have been updated since the last time stamp relating to the mobile station and sending the second paging message to the cells having being updated after the last time stamp relating to the mobile station. The inventive concept can be implemented for performing paging of mobile stations for packet data communication but also for voice paging messages on the functional channels. It is an advantage of the invention that the risk of loosing a mobile station after a cell update is minimized. A further advantage of the invention is that the implementation is easy. It is also an advantage that actually no broadcast messages are needed due to cells being updated, but alternatively the concept can also be used as a fallback if a mobile station would miss some broadcast information. Furthermore it is an advantage that the radio traffic is reduced since there is no need to send broadcast messages as soon as a cell is updated. The invention can be implemented in any cellular communication system supporting communication of packet data, such as GSM (Global System for Mobile Communications) GPRS (General Packet Radio Service), P-PDC (Packet-PDC), packet data service in ADCM, AMPS etc.